Abstract for gee_tr704

HOW DOES THE FEMORAL CORTEX DEPEND ON BONE SHAPE? A METHODOLOGY FOR THE JOINT ANALYSIS OF SURFACE TEXTURE AND SHAPE

A.H. Gee, G.M. Treece and K.E.S. Poole

15 June 2017

In humans, there is clear evidence of an association between hip
fracture risk and femoral neck bone mineral density, and some evidence
of an association between fracture risk and the shape of the proximal
femur. Here, we investigate whether the femoral cortex plays a role in
these associations: do particular morphologies predispose to weaker
cortices? To answer this question, we used cortical bone mapping to
measure the distribution of cortical mass surface density (CMSD,
mg/cm2) in a cohort of 125 females. Principal component analysis of
the femoral surfaces identified three modes of shape variation
accounting for 65% of the population variance. We then used
statistical parametric mapping (SPM) to locate regions of the cortex
where CMSD depends on shape, allowing for age. Our principal findings
were increased CMSD with increased gracility over much of the proximal
femur; and decreased CMSD at the superior femoral neck, coupled with
increased CMSD at the calcar femorale, with increasing neck-shaft
angle.

In obtaining these results, we studied the role of spatial
normalization in SPM, identifying systematic misregistration as a
major impediment to the joint analysis of CMSD and shape. Through a
series of experiments on synthetic data, we evaluated a number of
registration methods for spatial normalization, concluding that only
those predicated on an explicit set of homologous landmarks are
suitable for this kind of analysis. The emergent methodology amounts
to an extension of Geometric Morphometric Image Analysis to the domain
of textured surfaces, alongside a protocol for labelling homologous
landmarks in clinical CT scans of the human proximal femur.

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